[PATCH v6 0/2] perf tests: mmap-basic: fix user rdpmc detection logic

[PATCH v6 0/2] perf tests: mmap-basic: fix user rdpmc detection logic

[James Clark]

I'm sending this to fix the comments that I left on the "V3 resend"
because I don't think Qiao sent a V4 and it's been quite a while.

There were also some unreported bugs that I found during testing.

Changes in v6:
- Also skip on EROFS if sysfs was mounted as read-only
- Don't perf_evsel__delete() on NULL evsels
- Don't try to write or restore if the read failed
- Use existing "goto cleanup" pattern instead of continue
- Link to v5: https://patch.msgid.link/20261006-rdpmc-detection-logic-v5-0-b25c9d49baa1@linaro.org

Changes in v5:
- Keep rdpmc_supported variable name.
- Keep enum instead of int.
- Remove #ifdef __aarch64__ in the capability tests that made the
  cap_user_rdpmc test diverge. Now cap_user_rdpmc and pc->index are
  tested in the same way for all architectures that support user rdpmc.
- Disable running the 'enabled' version for unsupported arches which was
  equivalent to running the 'disabled' one twice and to be able to
  simplify the test.
- Link to v4: https://patch.msgid.link/20260817-rdpmc-detection-logic-v4-1-c22074578f6a@linaro.org

Changes in V4:
 - Don't remove pc->index check. Without it Perf can silently fall back
   to the read() syscall and the test is useless.
 - Test the 'expected disabled' case for Arm in an ifdef to workaround
   platform differences.
 - lseek() before writing to perf_user_access otherwise it's ignored.
 - Support restoring arbitrary values to perf_user_access because RISC-V
   uses '2' for legacy mode.
 - Rename rdpmc_supported to rdpmc_expected as this is what the test
   expects, not what the system does.
 - Label pc->index as rdpmc_event_active for clarity.
 - Add comments and simplify the commit message.

Signed-off-by: James Clark <james.clark@linaro.org>
---
James Clark (2):
      perf tests: mmap-basic: Only test userspace reading on supported platforms
      perf tests: mmap-basic: fix user rdpmc detection logic

 tools/perf/tests/mmap-basic.c | 188 +++++++++++++++++++++++++-----------------
 1 file changed, 113 insertions(+), 75 deletions(-)
---
base-commit: 1dc462fc214907671600172280c2e79ef9fe6fcf
change-id: 20260817-rdpmc-detection-logic-d3f7a49cfb46

Best regards,
--  
James Clark <james.clark@linaro.org>

[PATCH v6 1/2] perf tests: mmap-basic: Only test userspace reading on supported platforms

[James Clark]

mmap_user_read_instr() and mmap_user_read_instr_disabled() are the same
test for platforms that libperf doesn't support userspace counter
reading for. Only run the 'enabled' test for platforms that do support
it in order to simplify it in the next commit and not run the same test
twice. The test can then assert stronger guarantees and have fewer edge
cases to handle as we know it only runs in places where
'rdmpc_supported' will be true.

"unsupported" hasn't been a relevant skip reason since
commit 588d22b40480 ("perf test: Expand user space event reading (rdpmc)
tests") added the UNKNOWN fallback for unsupported platforms. Remove it
and leave only "permissions".

Signed-off-by: James Clark <james.clark@linaro.org>
---
 tools/perf/tests/mmap-basic.c | 51 ++++++++++++++++---------------------------
 1 file changed, 19 insertions(+), 32 deletions(-)

diff --git a/tools/perf/tests/mmap-basic.c b/tools/perf/tests/mmap-basic.c
index 5cec7644952c..208cd889f23d 100644
--- a/tools/perf/tests/mmap-basic.c
+++ b/tools/perf/tests/mmap-basic.c
@@ -378,13 +378,13 @@ static int test_stat_user_read(u64 event, enum user_read_state enabled)
 	return ret;
 }
 
-static int test__mmap_user_read_instr(struct test_suite *test __maybe_unused,
+static int __maybe_unused test__mmap_user_read_instr(struct test_suite *test __maybe_unused,
 				      int subtest __maybe_unused)
 {
 	return test_stat_user_read(PERF_COUNT_HW_INSTRUCTIONS, USER_READ_ENABLED);
 }
 
-static int test__mmap_user_read_cycles(struct test_suite *test __maybe_unused,
+static int __maybe_unused test__mmap_user_read_cycles(struct test_suite *test __maybe_unused,
 				       int subtest __maybe_unused)
 {
 	return test_stat_user_read(PERF_COUNT_HW_CPU_CYCLES, USER_READ_ENABLED);
@@ -406,42 +406,29 @@ static struct test_case tests__basic_mmap[] = {
 	TEST_CASE_REASON("Read samples using the mmap interface",
 			 basic_mmap,
 			 "permissions"),
-	TEST_CASE_REASON_EXCLUSIVE("User space counter reading of instructions",
-			 mmap_user_read_instr,
+
 #if defined(__i386__) || defined(__x86_64__) || defined(__aarch64__) || \
 			 (defined(__riscv) && __riscv_xlen == 64)
-			 "permissions"
-#else
-			 "unsupported"
-#endif
-		),
+	/*
+	 * libperf only supports userspace read for these platforms, see
+	 * tools/lib/perf/mmap.c
+	 */
+	TEST_CASE_REASON_EXCLUSIVE("User space counter reading of instructions",
+				   mmap_user_read_instr,
+				   "permissions"),
 	TEST_CASE_REASON_EXCLUSIVE("User space counter reading of cycles",
-			 mmap_user_read_cycles,
-#if defined(__i386__) || defined(__x86_64__) || defined(__aarch64__) || \
-			 (defined(__riscv) && __riscv_xlen == 64)
-			 "permissions"
-#else
-			 "unsupported"
+				   mmap_user_read_cycles,
+				   "permissions"),
 #endif
-		),
+
+	/* Counter read via userpage fallback is supported on all platforms */
 	TEST_CASE_REASON_EXCLUSIVE("User space counter disabling instructions",
-			 mmap_user_read_instr_disabled,
-#if defined(__i386__) || defined(__x86_64__) || defined(__aarch64__) || \
-			 (defined(__riscv) && __riscv_xlen == 64)
-			 "permissions"
-#else
-			 "unsupported"
-#endif
-		),
+				   mmap_user_read_instr_disabled,
+				   "permissions"),
 	TEST_CASE_REASON_EXCLUSIVE("User space counter disabling cycles",
-			 mmap_user_read_cycles_disabled,
-#if defined(__i386__) || defined(__x86_64__) || defined(__aarch64__) || \
-			 (defined(__riscv) && __riscv_xlen == 64)
-			 "permissions"
-#else
-			 "unsupported"
-#endif
-		),
+				   mmap_user_read_cycles_disabled,
+				   "permissions"),
+
 	{	.name = NULL, }
 };
 

-- 
2.43.0

[PATCH v6 2/2] perf tests: mmap-basic: fix user rdpmc detection logic

[James Clark]

RISC-V and Arm control userspace counter access through
/proc/sys/kernel/perf_user_access. Add that as a fallback to
set_user_read() so the test can exercise both enabled and disabled
states on those platforms.

Document disabled, enabled and legacy states in user_read_state and fail
on values outside the known 0-2 range. Preserve and restore any value in
this range, rather than just 0 or 1.

Skip when the control files exist but can't be written to
(USER_READ_ERR_PERM). We can't rely on always being able to write to
them when an exclude_kernel=0 event can be opened because opening events
might succeed for non-root users when perf_event_paranoid=-1.

This test isn't run on unsupported platforms since the previous commit,
so we can simplify the following things:

 * Test that cap_user_rdpmc is always equal to the requested state
   rather than checking it only when disabled. As long as we stop
   setting the cap in the attr unconditionally on Arm, this is ok.

 * Remove the USER_READ_UNKNOWN/rdpmc_supported fallback in the checks.
   Now the expected state is always the one requested. USER_READ_UNKNOWN
   only controls whether to skip restoration of the state on unsupported
   platforms, so call it USER_READ_ERR_NO_FILE.

Signed-off-by: Qiao Zhao <qzhao@redhat.com>
[Re-write to fix bugs in set_user_read() and simplify tests]
Assisted-by: Codex:GPT-6.1-Sol
Signed-off-by: James Clark <james.clark@linaro.org>
---
 tools/perf/tests/mmap-basic.c | 137 +++++++++++++++++++++++++++++-------------
 1 file changed, 94 insertions(+), 43 deletions(-)

diff --git a/tools/perf/tests/mmap-basic.c b/tools/perf/tests/mmap-basic.c
index 208cd889f23d..2d892a51a7f4 100644
--- a/tools/perf/tests/mmap-basic.c
+++ b/tools/perf/tests/mmap-basic.c
@@ -2,6 +2,7 @@
 #include <errno.h>
 #include <inttypes.h>
 #include <stdlib.h>
+#include <unistd.h>
 
 #include <fcntl.h>
 #include <linux/err.h>
@@ -12,6 +13,8 @@
 #include <perf/evlist.h>
 #include <perf/mmap.h>
 
+#include <tools/config.h>
+
 #include "cpumap.h"
 #include "debug.h"
 #include "event.h"
@@ -182,50 +185,83 @@ static int test__basic_mmap(struct test_suite *test __maybe_unused, int subtest
 }
 
 enum user_read_state {
-	USER_READ_ENABLED,
-	USER_READ_DISABLED,
-	USER_READ_UNKNOWN,
+	USER_READ_ERR_PERM = -2,
+	USER_READ_ERR_NO_FILE = -1,
+
+	USER_READ_DISABLED = '0',
+	USER_READ_ENABLED = '1',
+#if defined(__i386__) || defined(__x86_64__) || (defined(__riscv) && __riscv_xlen == 64)
+	/* Unrestricted access on x86, legacy access on RISC-V. */
+	USER_READ_LEGACY = '2',
+#endif
+	USER_READ_MAX
 };
 
-static enum user_read_state set_user_read(struct perf_pmu *pmu, enum user_read_state enabled)
+static enum user_read_state user_read_file_op(int fd, enum user_read_state enabled)
 {
 	char buf[2] = {0, '\n'};
-	ssize_t len;
-	int events_fd, rdpmc_fd;
-	enum user_read_state old_user_read = USER_READ_UNKNOWN;
-
-	if (enabled == USER_READ_UNKNOWN)
-		return USER_READ_UNKNOWN;
-
-	events_fd = perf_pmu__event_source_devices_fd();
-	if (events_fd < 0)
-		return USER_READ_UNKNOWN;
+	ssize_t len = read(fd, buf, 1);
+	enum user_read_state old_user_read = USER_READ_ERR_NO_FILE;
 
-	rdpmc_fd = perf_pmu__pathname_fd(events_fd, pmu->name, "rdpmc", O_RDWR);
-	if (rdpmc_fd < 0) {
-		close(events_fd);
-		return USER_READ_UNKNOWN;
-	}
-
-	len = read(rdpmc_fd, buf, sizeof(buf));
-	if (len != sizeof(buf))
+	if (len <= 0) {
 		pr_debug("%s read failed\n", __func__);
+		goto out;
+	}
 
-	// Note, on Intel hybrid disabling on 1 PMU will implicitly disable on
-	// all the core PMUs.
-	old_user_read = (buf[0] == '1') ? USER_READ_ENABLED : USER_READ_DISABLED;
+	old_user_read = buf[0];
 
 	if (enabled != old_user_read) {
-		buf[0] = (enabled == USER_READ_ENABLED) ? '1' : '0';
-		len = write(rdpmc_fd, buf, sizeof(buf));
+		buf[0] = enabled;
+		lseek(fd, 0, SEEK_SET);
+		len = write(fd, buf, sizeof(buf));
 		if (len != sizeof(buf))
 			pr_debug("%s write failed\n", __func__);
 	}
-	close(rdpmc_fd);
-	close(events_fd);
+
+out:
+	close(fd);
 	return old_user_read;
 }
 
+static enum user_read_state set_user_read(struct perf_pmu *pmu,
+					  enum user_read_state enabled)
+{
+	int events_fd, fd;
+	enum user_read_state ret = USER_READ_ERR_NO_FILE;
+
+	if (enabled == USER_READ_ERR_NO_FILE || enabled == USER_READ_ERR_PERM)
+		return enabled;
+
+	events_fd = perf_pmu__event_source_devices_fd();
+	if (events_fd >= 0) {
+		fd = perf_pmu__pathname_fd(events_fd, pmu->name, "rdpmc", O_RDWR);
+		if (fd >= 0) {
+			/*
+			 * Note, on Intel hybrid disabling on 1 PMU will implicitly
+			 * disable on all the core PMUs.
+			 */
+			ret = user_read_file_op(fd, enabled);
+			close(events_fd);
+			return ret;
+		} else if (errno == EACCES || errno == EROFS) {
+			/* Permissions failure, flag the failure for a skip. */
+			close(events_fd);
+			return USER_READ_ERR_PERM;
+		}
+		close(events_fd);
+	}
+
+	/* Fallback: perf_user_access interface (arm64, riscv, or similar) */
+	fd = open("/proc/sys/kernel/perf_user_access", O_RDWR);
+	if (fd >= 0)
+		ret = user_read_file_op(fd, enabled);
+	else if (errno == EACCES || errno == EROFS)
+		ret = USER_READ_ERR_PERM;
+
+	return ret;
+}
+
+
 static int test_stat_user_read(u64 event, enum user_read_state enabled)
 {
 	struct perf_pmu *pmu = NULL;
@@ -246,9 +282,6 @@ static int test_stat_user_read(u64 event, enum user_read_state enabled)
 			.config	= perf_pmus__supports_extended_type()
 			? event | ((u64)pmu->type << PERF_PMU_TYPE_SHIFT)
 				: event,
-#ifdef __aarch64__
-			.config1 = 0x2,		/* Request user access */
-#endif
 		};
 		struct perf_evsel *evsel = NULL;
 		int err;
@@ -256,8 +289,28 @@ static int test_stat_user_read(u64 event, enum user_read_state enabled)
 		bool mapped = false, opened = false, rdpmc_supported;
 		struct perf_counts_values counts = { .val = 0 };
 
+		if (__is_defined(__aarch64__) && enabled == USER_READ_ENABLED)
+			attr.config1 = 0x2;  /* Request user access */
 
 		pr_debug("User space counter reading for PMU %s\n", pmu->name);
+
+		if (saved_user_read_state == USER_READ_ERR_PERM) {
+			pr_debug("User space counter reading for PMU %s [Failed to get user read state]\n",
+				 pmu->name);
+			ret = TEST_SKIP;
+			goto cleanup;
+		}
+
+		/* Check value is in the expected range */
+		if (saved_user_read_state != USER_READ_ERR_NO_FILE &&
+		    (saved_user_read_state < USER_READ_DISABLED ||
+		     saved_user_read_state >= USER_READ_MAX)) {
+			pr_err("User space counter reading for PMU %s [Unexpected current state %d]\n",
+				pmu->name, saved_user_read_state);
+			ret = TEST_FAIL;
+			goto cleanup;
+		}
+
 		/*
 		 * Restrict scheduling to only use the rdpmc on the CPUs the
 		 * event can be on. If the test doesn't run on the CPU of the
@@ -301,21 +354,18 @@ static int test_stat_user_read(u64 event, enum user_read_state enabled)
 			goto cleanup;
 		}
 
-		if (saved_user_read_state == USER_READ_UNKNOWN)
-			rdpmc_supported = pc->cap_user_rdpmc && pc->index;
-		else
-			rdpmc_supported = (enabled == USER_READ_ENABLED);
+		rdpmc_supported = (enabled == USER_READ_ENABLED);
 
-		if (rdpmc_supported && (!pc->cap_user_rdpmc || !pc->index)) {
-			pr_err("User space counter reading for PMU %s [Failed unexpected supported counter access %d %d]\n",
-				pmu->name, pc->cap_user_rdpmc, pc->index);
+		if (rdpmc_supported && !pc->index) {
+			pr_err("User space counter reading for PMU %s [index must be set when enabled %d]\n",
+				pmu->name, pc->index);
 			ret = TEST_FAIL;
 			goto cleanup;
 		}
 
-		if (!rdpmc_supported && pc->cap_user_rdpmc) {
-			pr_err("User space counter reading for PMU %s [Failed unexpected unsupported counter access %d]\n",
-				pmu->name, pc->cap_user_rdpmc);
+		if (rdpmc_supported != pc->cap_user_rdpmc) {
+			pr_err("User space counter reading for PMU %s [cap should match requested state %d %d]\n",
+				pmu->name, pc->cap_user_rdpmc, rdpmc_supported);
 			ret = TEST_FAIL;
 			goto cleanup;
 		}
@@ -363,7 +413,8 @@ static int test_stat_user_read(u64 event, enum user_read_state enabled)
 			perf_evsel__munmap(evsel);
 		if (opened)
 			perf_evsel__close(evsel);
-		perf_evsel__delete(evsel);
+		if (evsel)
+			perf_evsel__delete(evsel);
 
 		/* If the affinity was changed, then put it back to all CPUs. */
 		if (pmu->cpus != NULL) {

-- 
2.43.0

Re: [PATCH v6 2/2] perf tests: mmap-basic: fix user rdpmc detection logic

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] perf tests: CPU affinity reset to all CPUs on early skip
--

commit 2dbb7615f7e3bec6f5e3a6ddba0d0fa138ec8fc9
Author: James Clark <james.clark@linaro.org>

perf tests: mmap-basic: fix user rdpmc detection logic

This commit introduces a fallback in set_user_read() to handle user counter
access on RISC-V and Arm through /proc/sys/kernel/perf_user_access. It also
refactors how the user_read_state is verified, adding early test skips when
these sysfs files return permission errors. Finally, it simplifies the
checks around cap_user_rdpmc to ensure the state matches what was requested.

> diff --git a/tools/perf/tests/mmap-basic.c b/tools/perf/tests/mmap-basic.c
> index 208cd889f23db..2d892a51a7f43 100644
> --- a/tools/perf/tests/mmap-basic.c
> +++ b/tools/perf/tests/mmap-basic.c
> @@ -256,8 +289,28 @@ static int test_stat_user_read(u64 event, enum user_read_state enabled)
>  		bool mapped = false, opened = false, rdpmc_supported;
>  		struct perf_counts_values counts = { .val = 0 };
>  
> +		if (__is_defined(__aarch64__) && enabled == USER_READ_ENABLED)
> +			attr.config1 = 0x2;  /* Request user access */
>  
>  		pr_debug("User space counter reading for PMU %s\n", pmu->name);
> +
> +		if (saved_user_read_state == USER_READ_ERR_PERM) {
> +			pr_debug("User space counter reading for PMU %s [Failed to get user read state]\n",
> +				 pmu->name);
> +			ret = TEST_SKIP;
> +			goto cleanup;
> +		}
> +
> +		/* Check value is in the expected range */
> +		if (saved_user_read_state != USER_READ_ERR_NO_FILE &&
> +		    (saved_user_read_state < USER_READ_DISABLED ||
> +		     saved_user_read_state >= USER_READ_MAX)) {
> +			pr_err("User space counter reading for PMU %s [Unexpected current state %d]\n",
> +				pmu->name, saved_user_read_state);
> +			ret = TEST_FAIL;
> +			goto cleanup;
> +		}
> +
>  		/*
>  		 * Restrict scheduling to only use the rdpmc on the CPUs the
>  		 * event can be on. If the test doesn't run on the CPU of the

[ ... ]

> @@ -363,7 +413,8 @@ static int test_stat_user_read(u64 event, enum user_read_state enabled)
>  			perf_evsel__munmap(evsel);
>  		if (opened)
>  			perf_evsel__close(evsel);
> -		perf_evsel__delete(evsel);
> +		if (evsel)
> +			perf_evsel__delete(evsel);
>  
>  		/* If the affinity was changed, then put it back to all CPUs. */
>  		if (pmu->cpus != NULL) {

[Severity: Low]
Does this code inadvertently broaden the process's CPU affinity when the PMU
iteration is skipped early?

When test_stat_user_read() jumps to cleanup due to a permission error or
invalid state, the thread's affinity was never narrowed to the PMU's CPUs
since the narrowing happens further down in the loop.

However, since the cleanup block unconditionally resets the CPU affinity to
all online CPUs if pmu->cpus is not NULL, could this override any
pre-existing affinity constraints the test process might have had?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261007-rdpmc-detection-logic-v6-0-d7ed6a85f864@linaro.org?part=2

Re: [PATCH v6 1/2] perf tests: mmap-basic: Only test userspace reading on supported platforms

[sashiko-bot]

> mmap_user_read_instr() and mmap_user_read_instr_disabled() are the same
> test for platforms that libperf doesn't support userspace counter
> reading for. Only run the 'enabled' test for platforms that do support
> it in order to simplify it in the next commit and not run the same test
> twice. The test can then assert stronger guarantees and have fewer edge
> cases to handle as we know it only runs in places where
> 'rdmpc_supported' will be true.
> 
> "unsupported" hasn't been a relevant skip reason since
> commit 588d22b40480 ("perf test: Expand user space event reading (rdpmc)
> tests") added the UNKNOWN fallback for unsupported platforms. Remove it
> and leave only "permissions".
> 
> Signed-off-by: James Clark <james.clark@linaro.org>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261007-rdpmc-detection-logic-v6-0-d7ed6a85f864@linaro.org?part=1